The present invention relates to a magnetic tape driving portion of a magnetic recording and reproducing apparatus.
A block diagram of a tape driving system of a conventional magnetic recording and reproducing apparatus is shown in FIG. 4. 14 is an idler gear, 15 is a driving gear, 16 is a capstan motor, 17 is a feed reel, 18 is a take-up reel, 19 is an FG pulse generating portion of the feed reel, 20 is an FG pulse generating portion of the take-up reel, 21 is a control portion, 22 is a servomechanism portion, 23 is a driving portion at idler gear position, and 24 is an FG pulse generating portion of the capstan motor 16.
Operation of a driving system of the above constitution such as shown in FIG. 4 will hereafter be explained. When the driving system is being shifted from a state of stop of a tape to a state of quick forward driving and rewinding of a tape, the idler gear 14 is caused to be in contact with the driving gear 15 which is driven by the capstan motor 16. When the driving system is being shifted from a state of stop of a tape to a state of quick forward driving of a tape by the rotational direction of the driving gear 15, the idler gear 14 rotates in contact with the take-up reel 18, and when it is being shifted from a state of stop of a tape to a state of rewinding of a tape by the rotational direction of the driving gear 15, the idler gear 14 rotates in contact with the feed reel 17 so as to feed the tape into rewinding direction.
However, in a method such as that described above, the time required to change the rotational direction of the capstan motor 16 is indefinite and it is necessary to allow for a sufficiently long waiting period until the rotational direction has changed completely, which in turn results in that it takes a long time to shift from a state of stop of a tape to a state of quick forward driving or rewinding of a tape. If an attempt is made to reduce this shifting time by shortening the waiting time necessary to complete the changing of the rotational direction of the capstan motor 16, the idler gear 14 comes in contact with the driving gear 15 before the rotational direction of the capstan motor 16 has completely changed, causing the idler gear 14 to come into rotating contact with a reel on the opposite side of a desired reel (this state is hereafter referred to as the reverse rotating contact). Alternatively, even if the rotational direction of the capstan motor 16 is correct, there was an inconvenience in that defective operation of a mechanical portion sometimes causes locking of the idler gear 14 and the driving gear 15 or the reverse rotating contact.